1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a semiconductor by a chemical vapor deposition method using light.
2. Description of the Related Art
As a conventional example of this type of semiconductor manufacturing apparatus, there is known one illustrated in an explanatory view of FIG. 13 by way of example.
In the drawing, reference numeral 1 indicates a chamber used for the semiconductor manufacturing apparatus.
Reference numeral 2 indicates a transparent plate, which is made up of a transparent material such as quartz glass or synthetic quartz glass and allows light to pass therethrough.
Reference numerals 3 indicate light sources, which are stored in a lamp house 4 and emit light such as vacuum ultraviolet light, ultraviolet light necessary for chemical vapor deposition (hereinafter called “CVD”) using light.
Reference numeral 5 indicates a top or a top plate which is provided over the chamber 1 and to which the transparent plate 2 is attached.
Reference numeral 6 indicates a gas supply pipe which supplies a material gas composed of gas used as a film producing material such as tetraethoxyorthosilicate (Si(OC2H5)4 (hereinafter called TEOS), tetramethylorthosilicate (Si(OCH3)4) or the like, or additive gas such as oxygen to within the chamber 1.
Incidentally, the material gas varies according to the type of a film to be produced and might not contain the additive gas.
Reference numeral 7 indicates a wafer used as an object to be processed, which is formed of a material such as silicon, or germanium. The material for the wafer 7 may also be silicon carbide, gallium arsenide or the like in addition to the above. However, the material is not limited to the above examples if other materials available as semiconductor materials are used.
Reference numeral 8 indicates a stage which is attached to a post 9 and stored within the chamber 1. Further, the stage 8 has the wafer 7 placed thereon and fixed thereto to perform its positioning.
Reference numeral 10 indicates a cooling system which is connected to a cooling pipe 11 for cooling the stage 8. A coolant such as water or ethylene glycol introduced into the cooling pipe 11 circulates in the stage 8.
Reference numeral 12 indicates an exhaust chamber, which is connected to an unillustrated vacuum pump and adjusts the degree of vacuum in the chamber 1 by controlling the degree of opening of a valve 13 provided within the exhaust chamber 12.
When silicon (Si) is used as the wafer 7 and an oxide film is produced by a CVD method using vacuum ultraviolet light under the above configuration, the light source 3 is used as a xenon (Xe2) excimer lamp and applies vacuum ultraviolet light therefrom. A material gas composed of TEOS and oxygen (O2) used as the additive gas is supplied to within the chamber 1 through the gas supply pipe 6 at a predetermined flow rate and sucked by the unillustrated vacuum pump through the exhaust chamber 12. The valve 13 is then adjusted to keep the pressure in the chamber 1 at a predetermined degree of vacuum.
Since, at this time, the temperature of the wafer 7 rises due to radiant heat of the light source 3, reaction heat of the material gas, or the like, the wafer 7 is cooled by the coolant introduced from the cooling system 10 through the cooling pipe 11 so as to be always kept at a suitable temperature, e.g., 25° C.
The above state is kept for a predetermined production time. Consequently, TEOS is decomposed at room temperature so that an oxide film such as a silicon dioxide (SiO2) film is grown on the wafer 7.
In the above-described related art, however, the film is formed not only on the wafer 7 but also on the transparent plate 2. Thus, fogging occurs in the transparent plate 2, so that the transmission of the vacuum ultraviolet light is inhibited.
Therefore, a problem arises in that the rate of production of the film on the wafer 7 is degraded and the thickness of the film varies between respective deposition operations, thereby destabilizing the quality of the film thickness between individuals.
Also a problem arises in that the stabilization of the quality of the film thickness needs to increase the frequency of replacement of the transparent plate 2 with another, and production lines must be stopped frequently for its replacement, thereby degrading production efficiency.
Further, since a step is formed between the transparent plate 2 for allowing the vacuum ultraviolet light to pass therethrough and the top plate 5 of the chamber 1 and shaped in a downwardly-extending convex form, the distribution of concentration of the material gas between the transparent plate 2 and the wafer 7 becomes ununiform.
As a result, a problem arises in that the film produced on the wafer 7 results in a distribution state in which the center thereof is thick and its peripheral portion is thin, thus impairing in-plane thickness uniformity. Further, a problem arises in that a product yield of each semiconductor fabricated from one wafer 7 is degraded so that production efficiency is decreased. This phenomenon noticeably appears as the distance between the transparent plate 2 and the wafer 7 approaches or decreases.